Haemoglobin and Thalassaemia

Question 1

What are the common characteristics of RBC’s?

Answer 1

Carry oxygen
Contain hb
No nucleus or mitochondria
Carry CO2 from tissues to the lungs

Question 2

What is haemoglobin?

Answer 2

Only in RBC
Normal conc 120-165g/L
Free Hb in the blood would be very toxic as it would promote radicals
Contains approx 3.4 mg Fe

Question 3

When does hb synthesis occur?

Answer 3

65% erythroblast stage

35% reticulocyte stage

Question 4

What is the structure of hb?

Answer 4

4 globin chains - 2 alpha and 2 beta
At the centre is the haem molecule with iron at the centre

Haem- synthesised in mitochondria
Globin - synthesised in the ribosomes

Question 5

Describe the synthesis of the haemoglobin:

Answer 5

Taken into the cell by the transferrin …………………………………..

Question 6

Describe haem:

Answer 6

Also contained in other proteins
Same in all types of Hb
Combination of protoporphyrin ring with central iron atom 
Iron is in the ferrous form (Fe2+) 
Able to bind reversibly with oxygen 
Synthesised mainly in mitochondria 

Negative feedback regulation based on the enzyme ALAS

Question 7

Describe the synthesis of globin:

Answer 7

Various different types of chains - 8 functional globin chains : beta (beta, gamma, delta + epson chains –> chromosome 11) and alpha cluster (alpha + zeta chains –> chromosome 16)

Question 8

Describe the importance of the globin gene expression and switching:

Answer 8

Any defects in alpha globin changes in the embryo would lead to death in the embryo …………………………

If there was a defect in the beta globin chain this would manifest at 3-6 months of a child’s life –> there is time to treat the problem.

Question 9

What is the normal Hb in adults?

Answer 9

Hb A - 2 alpha and 2 beta
HbA2 - 2 alpha and 2 delta

There will still be some traces of fetal haemoglobin - 2 alpha and 2 gamma chains

Question 10

What is the globin structure?

Answer 10

Primary structure - 141 amino acids (alpha), 146 AA (non-alpha)

Secondary - 75% ………………………………………….

Question 11

How does the Hb molecule differ from oxygenated to deoxygenated environments?

Answer 11

Oxygenated = more open structure + no 2,3 DPG

Question 12

Describe the haemoglobin dissociation curve:

Answer 12

O2 carrying capacity of Hb at different PO2

Sigmoidal shape

Co-operativity - as one molecule binds more molecules can bind more easily

Look at p50 - Hb is half saturated with oxygen

Can drop the partial pressure of O2 but the level of Hb O2 carrying capacity can be compensated until a certain point.

Shifting left = Hb binds more readily (higher affinity) to but is released less - higher pH, low 2,3 DPG

Shifting right - Less affinity, released oxygen more readily. low pH, high CO2, high 2,3 DPG

Question 13

What are the two main groups of haemoglobinopathies?

Answer 13

Structural variants of Hb

Defects in globin chain synthesis

Question 14

What is thalassaemia?

Answer 14

Genetic defects in the globin chain synthesis - an inherited disorder.

There are two types - alpha and beta (depends on which chain is affected)

Question 15

What is the classification of thalassaemia?

Answer 15

Globin type affected

or

Clinically severity - minor, intermediate or major
–> transfusion dependant and transfusion independent is used now.

Question 16

What is beta thalassaemia?

Answer 16

Deletion or mutation in B globin chains which results in the reduced or absent production of B globin chians

Autosomal recessive

Beta+ = there is a mutation in the beta chain where Beta 0 = absent chains.

Mainly in arab and Mediterranean areas

Question 17

What is the lab diagnosis of beta thalassaemia?

Answer 17

Full blood count - microcytic hypochromic - mcv lower and increase in RBC

Film - target cells, polikiocytosis (different shaped blood cells) but no anisocytosis (different sized blood cells)

Hb electrophoresis - not definitive and difficult to make a diagnosis from this. Raised HbA2 in beta thalassaemia.

Globin chain synthesis - PCR, sanga sequencing - this is used for a definitive diagnosis.

Question 18

What is thalassaemia major?

Answer 18

carry 2 abnormal copies of the beta chain

Severe anaemia ………….

Pokiliocytosis, fragments, hypochromic, alpha chain precipitates

Question 19

What is the clinical presentation of thalassaemia major?

Answer 19

Chronic fatigue 
Failure to thrive
Delay in growth and puberty 
Splenomegaly 
Jaundice
Iron overload - due to regular blood transfusion + absorb more iron from the GI tract
Skeletal deformity
Liver failure 
Cardiac failure
Biliary sepsis

Question 20

What are the treatments of thalassaemia major?

Answer 20

Regular blood transfusions *
Iron chelation therapy *

^ two of the main treatments

Splenectomy 
Supportive medical care 
Hormone therapy - anterior pituitiary affected by the iron overload. 
Hydroxyurea boost HbF
Bone marrow transplant

Screen early and this would identify those affected–> most are done neonatally.

Question 21

Describe the new gene related blood transfusions:

Answer 21

Phenotyped red cells

Aim for pre-transfusion Hb 95-100 g/L

Silences beta globin and allows gamma globin to take over

Regular transfusion

Question 22

How is the infection risk managed?

Answer 22

Many organisms that thrive in iron can cause infection in those who have thalassaemia.

Yersonia + gram negative sepsis are treated with prophylaxis.

Question 23

What is iron chelation therapy?

Answer 23

…………..

Three main used clinically:
-DFO - subcutaneous IV , 8-12 hours , 5 days a week (Side effects: vertebral dysplasia, retinopathy , sensorinerural loss, yersina infection - vitamin c can help with the mobilisation of iron)

• Deferiprone - oral, 3 times a day (more effective in cardiac iron overload. Side effects: GI disturbance, hepatic impairment, neutropennia, agranulocytosis, zinc deficiency)
• Defarasirox - oral, once a day (Side effects: rash, GI symptoms, hepatitis and renal impairment)

Can give as a combined therapy.

Question 24

How can you monitor iron overload?

Answer 24

Serum ferritin - acute phase protein (only if less than 2500)

Liver biopsy - rare

T2 Cardiac and hepatic MRI

Ferriscan - R2 MRI

Question 25

What is alpha thalassaemia?

Answer 25

Deletion or mutation in a globin genes

Severity depends on the number of a globin genes that are affected

Excess beta and gamma chains form tetramers.

Reduced A2.

Question 26

What are the problems associated with treatment in developing countries?

Answer 26

Lack of awareness of the problems

Lack of experienced health care providers

Availability of blood

Cost and compliance with iron chelation

Availability of very high cost bone transplants

Question 27

What is the screening a prevention of thalassaemia?

Answer 27

Counselling and health education

Extend family screening

Antenatal screening

Pre-natal diagnosis (CVS)